The blast furnace method for the preparation of technical grade iron or pig iron from iron ore is based essentially on the reduction of iron oxide with carbon. The carbon employed is generally in the form of coke. Due to the cost and availability of coke, this material is often partially replaced by natural gas, coal, fuel oils, etc. It is noted that it is possible to inject pulverized coal, gases or liquid petroleum products into the furnace to promote indirect reduction, increase the blast furnace output, and decrease the consumption of coke, a material that is expensive to produce and desirable to replace. Many recent developments in blast furnace technology have been centered on methods to partially replace the expensive coke with less costly substitutes. However, with modern technology, coke can be replaced to only a given extent by a liquid fuel such as crude oil, tar, residual oil, or fuel oil. Introducing these materials into a blast furnace to reduce coke consumption calls for these materials to be atomized and blown into the furnace. Unfortunately, procedures of this type often give rise to considerable soot formation which is both undesirable from a pollution standpoint and which also upsets the equilibrium of the blast furnace process.
In the blast furnace process, iron bearing materials including iron ore, sinter, scrap, or other iron source along with a fuel, generally coke, and a flux, limestone, or dolomite are charged into the blast furnace from the top. The blast furnace burns part of the fuel to produce heat for melting the iron ore and the balance of the fuel is utilized for reducing the iron and its combination with carbon. The charge in a typical furnace, per ton of pig iron produced, is about 1.7 tons of ore or other iron bearing materials, 0.5-0.65 tons of coke or other fuel, and about 0.25 tons of limestone and/or dolomite. Additionally, from 1.8-2.0 tons of air are blown into the furnace during the process.
Pulverized coal injection has been used for many years to reduce the use of coke and to enhance the operation of blast furnaces in the manufacture of pig iron. The ability to replace coke with pulverized coal in a blast furnace may reduce pollution (as less coke is needed), and may reduce the costs associated with the manufacture of iron.
In practice, iron bearing raw materials (sinter, iron ore, pellets, etc.), fuel (coke), and flux (limestone, dolomite, etc.) are charged to the top of the furnace. Heated air (blast) is blown into a blast furnace through openings, known as tuyeres, at the bottom of the furnace. Tuyere stocks are fitted with injection lances through which supplemental fuels (gas, oil and pulverized coal) are injected. The blast air burns the fuel and facilitates the smelting chemistry that produces iron. Combustion gases from the blast furnace are scrubbed to remove particulate and other noxious gases before being burned in stoves which are used to preheat blast air or in other applications, e.g., coke ovens, boilers, etc.